Evolution and Themes in Biology

Opening Questions and the Study of Life

Biology is the scientific study of life, aiming to understand living organisms and their interactions. The study of life reveals several unifying themes that help organize biological knowledge.

• Organization: Life is structured in hierarchical levels, from molecules to the biosphere.

• Information: Genetic information is stored and transmitted in DNA.

• Evolution: Populations of organisms change over time through natural selection.

• Energy and Matter: Life requires energy transformation and matter cycling.

• Interactions: Organisms interact with each other and their environment.

Theme 1: New Properties Emerge at Successive Levels of Biological Organization

Complex properties result from the arrangement and interactions of parts at each level of organization.

• Biosphere: All life on Earth.

• Emergent Properties: For example, hydrogen and oxygen combine to make water; parts of a bicycle work together to enable movement.

• Reductionism: Studying simpler components to understand complex systems.

Theme 2: Life Processes Involve the Expression and Transmission of Genetic Information

Genetic information is encoded in DNA and transmitted from parent to offspring. Gene expression converts DNA information into cellular products.

• Chromosomes: Structures containing DNA and genes.

• Gene Expression: DNA is transcribed to RNA, then translated into proteins.

• Example: Crystallin protein in the eye lens is produced by gene expression.

Energy and Interactions in Ecosystems

Energy Flow and Chemical Cycling

Energy flows through ecosystems, while matter cycles among living and nonliving components.

• Producers: Organisms that make their own energy (e.g., plants).

• Consumers: Organisms that obtain energy by eating other organisms.

• Heat Loss: Energy is lost as heat during energy transformations.

Theme 4: From Molecules to Ecosystems, Interactions Are Important

Interactions occur at all levels, from molecules to ecosystems, and can be beneficial or harmful.

• Molecular Interactions: Regulation of cellular processes.

• Organismal Interactions: Competition, predation, symbiosis.

• Ecological Interactions: Affect population dynamics and ecosystem stability.

Diversity and Unity of Life

Classification and Domains

Life is classified into three domains based on genetic and cellular differences.

• Bacteria

• Archaea

• Eukarya: Includes plants, animals, fungi, and protists.

Evolution as a Core Theme

Evolution explains the unity and diversity of life. All living organisms are modified descendants of common ancestors.

• Natural Selection: Mechanism of evolution proposed by Charles Darwin.

• Adaptation: Traits that enhance survival and reproduction.

Scientific Inquiry and the Nature of Science

How Science Works

Science is a process for understanding natural phenomena through observation, hypothesis formation, experimentation, and analysis.

• Data: Quantitative (numerical) and qualitative (descriptive).

• Hypothesis: Testable explanation based on observations.

• Controlled Experiment: Compares an experimental group with a control group.

• Variables:

  • Independent Variable: Manipulated by the researcher.

  • Dependent Variable: Measured response.

• Scientific Theory: Broad explanation supported by a large body of evidence.

Chemistry of Life

Elements, Compounds, and Chemical Bonds

All matter is composed of elements, which combine to form compounds through chemical bonds.

• Element: Substance that cannot be broken down by chemical means.

• Compound: Substance formed by two or more elements in a fixed ratio.

• Chemical Bonds: Forces that hold atoms together (ionic, covalent, hydrogen).

Atomic Structure and Isotopes

Atoms consist of a nucleus (protons and neutrons) and electrons in shells. Isotopes are atoms of the same element with different numbers of neutrons.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Number of protons plus neutrons.

• Isotope Example: Carbon-12, Carbon-13, Carbon-14.

Electron Configuration and Chemical Properties

The chemical properties of an atom are determined by its electron configuration, especially the valence electrons in the outermost shell.

• Valence Electrons: Electrons in the outermost shell; determine bonding behavior.

• Electron Shells: First shell holds 2 electrons, second shell holds up to 8.

Chemical Bonds

• Covalent Bonds: Atoms share electrons to fill their valence shells.

  • Single Bond: One pair of shared electrons.

  • Double Bond: Two pairs of shared electrons.

  • Nonpolar Covalent: Electrons shared equally (e.g., H2, CH4).

  • Polar Covalent: Electrons shared unequally (e.g., H2O).

• Ionic Bonds: Attraction between positively and negatively charged ions (e.g., NaCl).

• Hydrogen Bonds: Weak attraction between a hydrogen atom carrying a partial positive charge and an electronegative atom (e.g., oxygen in water).

Water: Properties and Importance

Water is a polar molecule with unique properties essential for life.

• Cohesion: Water molecules stick together via hydrogen bonds.

• Adhesion: Water molecules stick to other substances.

• Moderation of Temperature: Water absorbs and releases heat slowly.

• Expansion upon Freezing: Ice is less dense than liquid water.

• Excellent Solvent: Water dissolves many substances.

Acids, Bases, and pH

Acids and bases affect the concentration of hydrogen ions in solution, influencing pH.

• Acids: Proton donors; increase H+ concentration.

• Bases: Proton acceptors; decrease H+ concentration.

• pH Scale: Measures acidity or alkalinity; pure water has pH 7.

Carbon: The Backbone of Life

Carbon atoms can form four covalent bonds, allowing for a diversity of organic molecules.

• Bonding Versatility: Can bond with hydrogen, oxygen, nitrogen, and itself.

• Single, Double, Triple Bonds: Carbon can form single, double, and triple covalent bonds.

• Organic Compounds: Molecules containing carbon (e.g., urea).

Key Equations

• Atomic Number:

• Mass Number:

Additional info:

• Some context and examples have been expanded for clarity and completeness.

• Tables and diagrams have been described in text and HTML format for accessibility.